Luminance

Four examples of the Uniformity illusion with luminance as an example.

Open the video fullscreen.

Keep your eyes fixated on the centre of the screen for a good amount of time (tens of seconds to minutes).

The first two examples contain no fixation spot, the latter two are identical to the first two, but they do contain a fixation spot. Some people find that the illusion works better without a fixation spot, but you can try out which works best for yourself.

For more information, see the text below the examples.

More information: In all examples the luminance of the periphery is identical. The first two examples are the same as the last two, but the last two have a fixation spot. In the first example the central patch is darker than the peripheral patch. If you watch this example full screen, and you fixate your eyes on the centre of the screen for a prolonged period of time (several tens of seconds) you will see the illusion wane in and out of existence. Sometimes some parts of the periphery turn darker, sometimes the entire screen takes on the luminance of the central patch. In the second example the periphery is identical, but now the central patch is lighter. Now the periphery never becomes darker. However, at moments, some parts of the periphery, or all of it, will take on the luminance of the central patch.

Fixating your eyes on the centre of the screen while you are attending to the periphery can be challenging, and may need some practicising.

Why the illusion wanes in and out is not exactly known, but one option is that the illusion is mainly driven by predictive coding. Staring for a long time at the centre deteriorates peripheral information more than central information. Rather than leaving information incomplete, the brain fills in the gaps with good guesses. In this case the assumption of surface uniformity and good central information. So the illusion becomes stronger when peripheral information fades out, but it may become weaker when eye blinks, or small eye movements, temporarily increase the quality of peripheral information.